The goal of this project is to investigate the molecular mechanisms underlying the malignant transformation of cells. We have been studying the structure and function of the tumor antigen (T-antigen) encoded by simian virus 40 (SV40). Using either recombinant viruses which contain different parts of the T-antigen gene or proteolytic enzymes which cleave the T-antigen molecule at specific sites, we were able to dissect and identify the roles of the various domains of this multifunctional SV40 T-antigen.